Complementary role of MRI after sonography in assessing bilateral urinary tract anomalies in the fetus

OBJECTIVE. The objectives of our study were to evaluate the contribution of adding MRI findings to inconclusive sonographic data when assessing fetal urinary tract anomalies and to determine how this addition may affect the management of pregnancy. SUBJECTS AND METHODS. We prospectively used MRI to study 16 third-trimester fetuses in whom sonography suggested bilateral urinary tract anomalies but failed to provide a definite diagnosis. These anomalies included enlarged hyperechoic kidneys (n = 6), bilateral pelvicaliceal dilatation (n = 6), renal cystic lesions (n = 2), and renal agenesis associated with. severe oligohydramnios (n = 2). RESULTS. The addition of MRI to sonography modified the diagnosis in five fetuses. In a fetus with suspected bilateral ureteropelvic obstruction, the diagnosis of bilateral ureterohydronephrosis associated with reflux or ureterovesical junction obstruction was made. In a fetus with an enlarged bladder at 32 weeks' gestational age, a possible diagnosis of megacystic microcolon was excluded on the basis of the normal appearance of the colon. In two fetuses with enlarged hyperechoic kidneys, MRI showed localized medullary hyperintense lesions suggesting autosomal recessive polycystic kidney disease in one fetus and medullary cystic dysplasia in another fetus with Jeune's syndrome. In a patient with suspected unilateral renal agenesis, MRI showed bilateral agenesis. In four fetuses, the addition of MRI to sonography led to a diagnosis that modified the decision to continue or terminate the pregnancy. CONCLUSION. MRI can accurately show many urinary tract anomalies in third-trimester fetuses. It may be a useful complementary tool in the assessment of bilateral urinary tract anomalies of fetuses, particularly in cases with inconclusive sonographic findings.